1. Field of the Invention
This invention relates generally to the field of laboratory devices for infusing and monitoring small animals. More particularly, the invention concerns a laboratory device for passing multiple channels, without any form of commutation, to a tethered animal in a stationary environment, the device being responsive to a motion of the animal to reduce torque on the animal.
2. Background of the Related Art
Physiological studies often require externalization and attachment of implanted fluid filled catheters and/or electrical lines. Initially, to prevent tangling of these lines, an awake animal experiment required rotational restraint of the animal. To achieve a more normal, stress free environment, fluid and electrical swivels were developed that allowed a singly housed animal to move freely about the cage and line tangling was prevented by virtue of the swivels. The animal provides the requisite torque to rotate such devices.
While prior art electrical swivels have been built with a large number of electrical lines that a small animal is capable of turning, this has not been the case with fluid swivels. Small animals, such as rats, have difficulty turning a swivel with more than two fluid channels due to the build up of seal torques. Applications, such as brain microdialysis, require two channels per microdialysis probe. Therefore, to use two or more probes requires four or more channels. Not only does the rotational torque become excessive, it is difficult to achieve the low dead volume requirement on all channels. Electrical swivels have been combined with fluid swivels but the practical limit at the present time remains at two fluid lines with rats and one with mice.
These problems are further aggravated when two or more fluid channels are provided in a swivel. Increasing the number of channels increases the probability of the swivel leaking or having a higher torque. Furthermore, there is an inverse relationship between torque and leakage. A solution to reduce leakage is to use a stronger seal but this also comes at the price of a higher torque.
Where the total torque requirement exceeds an animals ability, a solution has been attempted that allows the floor of the circular cage to rotate freely. Hence, as the animal attempts to turn, the floor moves instead. A powered version of this type of device is commercially available through Bioanalytical Systems, Inc. While this prevents tangling of lines, it provides abnormal sensory input to the animal and evokes treadmill type behavior.
Other systems employ a rotating platform above the cage containing the animal. The rotating platform contains the necessary equipment such as fluids, pumps, amplifiers and other electronic circuitry. This large mass must be rotated with the animal and significantly impairs the dynamic response of the system. Furthermore, connection to large devices is generally impossible without commutation.
One such device is disclosed in U.S. Pat. No. 5,305,712 ("Goldstein") which discloses a tether system for an animal. The disclosed tether system includes an area for the animal and a "structure" above the area with an anchor for preventing the entanglement of the fluid or power providing means as the animal moves about in a cage.
Therefore, there is a need for a device that would allow experimenters to run multiple lines or channels to an animal including electrical, fluid, optical lines, and any combinations thereof. The device needs to provide a normal sensory environment for the animal that does not impose excessive torque when the animal wishes to turn. The elimination of commutation would obviate any possible leaks in fluid lines and eliminate noise due to sliding contacts and permit optical fibers to be used. As studies involving genetically diverse mice become more prevalent, the ability to attach multiple lines to awake mice would be even more desirable